# Collier's New Encyclopedia (1921)/Sun, Parallax of the

**SUN, PARALLAX OF THE**, or
**SOLAR PARALLAX**, the angle
subtended by the radius of the earth at a
distance equal to that of the earth from
the sun. More exactly, it is the angle
subtended by the equatorial radius of the
earth at the mean distance of the sun,
though this would be called, when speaking
exactly, the mean equatorial
horizontal parallax of the sun. It is, as
nearly as we know it today, almost 8.8",
with an uncertainty of probably not more
than 0.01" or 0.02" different from this
in either direction. This corresponds to
a distance of the sun a little less than
93,000,000 miles. More time, labor, and
money have been expended in the
determination of the polar parallax than
of any other astronomical constant, on
account of its importance in giving us an
accurate base line with which to gauge
the solar system and then strike out into
the depths of stellar space. Before the
last transit of Venus it was thought that
careful observation would give an exceedingly
accurate value of this constant; but
these hopes were disappointed, and it is
known that we have at hand at any time
more accurate methods of determining
the distance of the sun than from any
possible observation of a transit of
Venus. The most accurate direct method
is likely to be the direct measurement of
the parallax of the nearer and brighter
asteroids by the heliometer.